1. Field of the Invention
The present invention relates to a muting device, which may be utilized in a grand piano and which reduces normal tone volume of a piano sound when depressing a key of the piano.
2. Prior Art
FIG. 1 illustrates an example of the mechanical construction of the known key driving unit provided in a grand piano.
Before describing the conventional muting device, simple description will be given with respect to the key driving unit in conjunction with FIG. 1. Herein, 1 designates a key which is provided on a board 2 such that it can freely revolve about an axis "X" in vertical direction. The right side of FIG. 1, designates a front side of key 1 and the left side designates a back side of the key 1. On a support rail 3 positioned at the back side of the key 1, a support 4 is provided such that it can freely revolve about a pin 4a in vertical direction. Next, a support heel 5 is attached at the lower surface of the support 4 and it is positioned to be in contact with a capstan screw 4, so that an angular position of the support 4 is set. A swing edge portion of the support 4 is supported by a jack 7 which can be freely swung about a pin 7a.
In addition, 9 designates a shank rail to which a shank frange 10, is fixed. Further, a hammer 11 is attached to the shank frange 10, so that it can freely swing about a pin 11a provided at an edge portion of the shank frange 10. The hammer 11 is constructed by a hammer felt 13 and a shank portion 14. This hammer felt 13 strikes a string 12, while the shank portion 14 supports the hammer felt 13. When the key 1 is depressed, an edge portion of the jack 7 pushes the shank portion 14 via a roller 15 in an upward direction so that the shank portion 14 rotates.
Incidentally, 17 designates a damper which is operated by a back edge portion (not shown) of the key 1 by means of a damper lever 18 and a damper wire 19.
In the above-mentioned key driving unit, when the key 1 is depressed, the key 1 rotates about an axis X in a clockwise direction. Associated with the rotary movement of the key 1, the lower surface of the support 4 is pushed upward by the capstan screw 6 and support heel 5 so that the support 4 rotates about the pin 4a in a counterclockwise direction. Due to this rotation of the support 4, the hammer shank portion 14 is pushed upward by means of the jack 7 and roller 15. As a result, the hammer 11 rotates about the pin 11a in a clockwise direction, so that its hammer felt 13 strikes the string 12, by which the piano sound is generated.
During generation of the piano sound, the damper 17 is operated by the back edge portion of the key 1 by means of the damper lever 18 and damper wire 19 so that it is lifted up. Then, the depressing pressure applied to the key 1 is released so that the key 1 is returned to its original position. At this time, the damper 17 falls downward and thereby touches with the string 12 so that generation of the piano sound is suspended.
FIG. 2 illustrates positional relationship between the key 1 and support 4.
Herein, the support 4 is moved accompanied with the key depression as described above. In addition, the front side portion of the key 1 is moved in connection with the swing edge portion of the support 4 (see pin 7a which supports the jack 7) as shown in FIG. 3. As shown in FIG. 3, upward movement of the swing edge portion of the support 4 is increased proportional to the downward movement of the front side portion of the key 1.
The upward movement of the pin 7a depends on balance ratio A:B of the key 1 and balance ratio C:D of the support 4. Herein, "A" designates distance between the front edge of key 1 and supporting point X, while "B" designates distance between the supporting point X and capstan screw 6. In addition, "C" designates distance between the rotation center 4a of the support 4 and the point at which the support 4 contacts with the capstan screw 6, while "D" designates distance between the rotation center 4a and pin 7a.
According to a first mechanism employed in the conventional muting device, the position of the hammer 11 is shifted in a horizontal direction (i.e., key disposing direction in the keyboard of the piano) so as to reduce the number of the strings to be struck so that the tone volume is muted.
According to a second simple mechanism employed in the conventional muting device, a muffler felt and the like is inserted between the string 12 and hammer 11 so as to reduce the striking force of the hammer 11.
In the above-mentioned first mechanism of the conventional muting device, the tone color can be changed. However, there is a drawback in that the tone volume cannot be always reduced.
In the second mechanism of the conventional muting device, the tone volume can be reduced in the higher pitch range. However, the tone volume in the middle lower pitch ranges cannot be reduced to the expected level. In addition, the tone color of the overtone having a higher harmonic frequency is muted, thus, there is a drawback in that the muted sound must be heard without tension. Moreover, when simulating the muting operation of the foregoing muffler felt in the automatic performance apparatus, it is impossible to reproduce the muting effect due to the reaction of the felt, which deteriorates the simulation accuracy of the automatic performance apparatus.
Most of the upright pianos employ the muting device having the mechanism in which, to reduce the string-striking-distance, the hammer 11 is positioned closer to the string 12. If such muting device is employed in the grand piano, reaction force of the hammer 11 cannot be transmitted to the key 1, so that due to the weight balance of the key 1, the back portion of the key 1 with respect to the supporting point X is lifted up. Thus, the back edge portion of the key 1 lifts up the damper lever 18, which raises a drawback in that the damper function cannot be accomplished. In an initial state of the key depression, the hammer 11 does not move (which is called "lost motion"), which raises another drawback in that the key touch feeling is deteriorated.